1. Field of the Invention
The present invention relates to a load driving device that drives and controls a load having an inductance component (e.g., a motor coil that constitutes a motor) and to an electrical apparatus that uses the load driving device.
2. Description of Related Art
FIG. 4 is a block diagram showing a conventional example of a motor driving device.
As shown in FIG. 4, the conventional motor driving device includes a driver DRV that supplies a drive current Im to a motor M, a current sensing resistor RNF that generates a sensed voltage Vadj corresponding to switching current flowing in the driver DRV (i.e., corresponding to the drive current Im), a comparator CMP that compares the sensed voltage Vadj with a predetermined reference voltage Vref and a control circuit CTRIJ that generates a drive control signal for the driver DRV based on a comparison output signal Sx of the comparator CMP, so as to perform constant-current chopping control (on and off control) of the drive current Im.
As conventional techniques related to the above description are disclosed in JP-A-H11-299283, JP-A-H8-33382 and the like.
JP-A-H11-299283, which is filed by the same applicant as the present application, discloses a sensorless motor driver including a comparator circuit that compares a counter electromotive voltage generated by each phase of a brushless motor with a neutral voltage of the phase so as to generate a rectangular wave signal, a mask circuit that masks the rectangular wave signal with a noise mask signal having a noise mask period, a mask signal generating circuit that generates the noise mask signal, a drive signal forming portion that forms a drive signal based on the rectangular wave signal masked by the mask circuit and a current supplying portion that supplies a drive current to the brushless motor based on the drive signal. This sensorless motor driver further includes a current sensing portion that senses the drive current and a portion that changes the noise mask period based on an output signal of the current sensing portion.
JP-A-H8-33382 discloses a driving device of a brushless motor including a plurality of driving transistors that supply the drive current to a plurality of phases of motor drive coils, a torque command signal generating circuit that senses the motor drive current so as to generate a torque command signal, a current distributing circuit that supplies current in accordance with an output signal of the torque command signal generating circuit to bases of the plurality of driving transistors sequentially, a trapezoidal wave current synthesizer that delivers the trapezoidal wave current to the current distributing circuit, a counter electromotive force detector that detects a counter electromotive force generated in the motor drive coil and shapes a waveform of the same and a mask signal generator that delivers a signal for masking a part of the signal waveform to the counter electromotive force detector.
The conventional motor driving device shown in FIG. 4 can surely maintain the drive current Im for the motor M at a desired value by the constant-current chopping control of the drive current Im.
However, the conventional motor driving device described above has a possibility of causing a malfunction in the constant-current chopping control of the drive current Im when a spike noise (a ringing noise) caused from switching operation of the driver DRV is added to the sensed voltage Vadj as shown in FIG. 5, so that the comparison output signal Sx of the comparator CMP changes to an unintentional wrong logic.
Note that each of the conventional techniques disclosed in JP-A-H11-299283 and JP-A-H8-33382 is a technique for masking noise in the counter electromotive voltage generated in the motor coil, and both documents do not disclose about the spike noise caused from the constant-current chopping control of the drive current or a malfunction caused from the spike noise.
In addition, each of the conventional techniques disclosed in JP-A-H11-299283 and JP-A-H8-33382 has a structure for masking process on the output signal of the comparator or the counter electromotive force detector, and the masking process should be performed until the output signal recovers from a wrong logical state to a correct logical state. Therefore, reduction of the mask period (i.e., improvement of chopping frequency) is restricted by an operational speed of the comparator.